The present document claims priority and contains subject matter related to Japanese Patent Application No. 2000-041135 filed in the Japanese Patent Office on February 18, 2000, and the entire contents of which is hereby incorporated herein by reference.
1. Field of the Invention
The present invention relates to an image developing device for use in image forming apparatuses, such as electrophotographic copying machines, facsimile machines, printers, etc., and more particularly to an image developing device and an image forming apparatus using the developing device to prevent toner from adhering to a developing sleeve of the developing device.
2. Discussion of the Background
In an image forming apparatus using electrophotography, it is well known to use two-component developer including carrier and toner for development. FIG. 5 schematically illustrates an image forming apparatus including a developing device using a two-component developer. FIG. 6 is a diagram for explaining an operation of the developing device.
In FIG. 5, a drum-like shaped photoconductor 101 is rotated in a counterclockwise direction indicated by an arrow by a driving device (not shown). Around the photoconductor 101 are arranged, a charging roller 102, an exposure device 103, a developing device 104, a transfer device 105, a cleaning device 106, and a discharging device 107.
The charging roller 102 uniformly charges the surface of the photoconductor 101. The exposure device 103 irradiates a laser light on the surface of the photoconductor 101, which has been uniformly charged by the charging roller 102, to form a latent image thereupon. The developing device 104 applies toner to the latent image on the surface of the photoconductor 101 to form a toner image. The transfer device 105 transfers the toner image to a transfer sheet. The cleaning device 106 removes residual toner remaining on the surface of the photoconductor 101 after transfer of the toner image to the transfer sheet. Thereafter, the discharging device 107 discharges the surface of the photoconductor 101, which has been cleaned by the cleaning device 106. The image forming apparatus then repeats each of the above-noted operations by the charging roller 102, the exposure device 103, the developing device 104, the transfer device 105, the cleaning device 106, and the discharging device 107 (i.e., a charging process, an exposure process, a developing process, a transfer process, a cleaning process, and a discharging process).
The developing device 104 includes a developer container 108 having an opening formed facing the photoconductor 101, a developing sleeve 109 arranged so as to face the photoconductor 101 in the developer container 108, and a two-component developer 110 accommodated in the developer container 108. The developing device 104 further includes a stirring member 111 configured to stir and to supply the developer 110 to the surface of the developing sleeve 109, and a doctor blade 112 configured to regulate the thickness of the developer 110 carried on the surface of the developing sleeve 109.
The developer 110 includes magnetic carrier and non-magnetic toner, which are mixed with each other. When the developer 110 is stirred by the stirring member 111, the toner of the developer 110 is charged by friction between the toner and the carrier. A magnet (not shown) is arranged within the developing sleeve 109. The developer 110 is held on the surface of the developing sleeve 109 by a magnetic force of the magnet. The developing sleeve 109 is rotated in a direction indicated by an arrow in FIG. 5, and the developer 110 held on the surface of the developing sleeve 109 is moved, after having its thickness regulated by the doctor blade 112, to a space between the photoconductor 101 and the developing sleeve 109. Toner adhered to the carrier held on the surface of the developing sleeve 109 is moved toward a latent image on the photoconductor 101 by an electric field formed between the developing sleeve 109 and the latent image on the photoconductor 101, so as to adhere to the latent image.
Generally, in digital image forming apparatuses using electrophotography, such as laser beam printers or digital copying machines, the photoconductor 101 is charged to the same polarity as that of the toner. When the toner has a negative charge, the electric potential of the photoconductor 101 is set, for example, to xe2x88x92950V, and an electric field is formed as illustrated in FIG. 6. A voltage of the same polarity as that of the toner (e.g., xe2x88x92600V) is applied to the developing sleeve 109. In this case, when the exposure device 103 irradiates a laser beam light to the surface of the photoconductor 101 which has been uniformly charged, the electric potential of non-image (background) parts of the surface of the photoconductor 101 is kept at xe2x88x92950V and the electric potential of image parts thereof is changed to about xe2x88x92100V. Therefore, the electric field between the developing sleeve 109 and the image parts of the photoconductor 101 is directed from the image parts of xe2x88x92100V to the developing sleeve 109 of xe2x88x92600V, and thereby the toner having a negative charge adheres to the image parts of the photoconductor 101. On the other hand, the electric field between the developing sleeve 109 and the non-image parts of the photoconductor 101 is directed from the developing sleeve 109 of xe2x88x92600V to the non-image parts of xe2x88x92950V. Therefore, the toner having a negative charge does not adhere to the non-image parts of the photoconductor 101.
The transfer device 105 transfers a toner image on the surface of the photoconductor 101 to a transfer sheet. The transfer sheet carrying the transferred toner image thereupon is conveyed to a fixing device (not shown). The fixing device fixes the toner image onto the transfer sheet by heating the toner image so as to be melted and by then applying a pressure to the toner image. The electric power consumed by the fixing device when heating and melting a toner image generally occupies a major part of the necessary power of an image forming apparatus.
Recently, from a view point of energy saving, it is desired to reduce power consumption in image forming apparatuses. For meeting such a demand for energy saving it is desired to reduce the temperature at a fixing device when heating and melting a toner image at the fixing device. For reducing the temperature at a fixing device when heating a toner image, the toner must be a type of toner capable of being fixed onto a transfer sheet at a relatively low temperature.
In image forming apparatuses, generally the electric potential difference between the developing sleeve 109 and the non-image parts of the photoconductor 101 is configured such that charged toner of the developer 110 carried on the developing sleeve 109 does not move to non-image (background) parts of the surface of the photoconductor 101. Rather, the electric field having a direction toward the developing sleeve 109 causes the toner to adhere to the developing sleeve 109. When the toner of the type that can be fixed onto a transfer sheet at a relatively high temperature, because of its relatively weak adhering force, even when the toner has once adhered to the developing sleeve 109, the adhered toner is easily removed from the developing sleeve 109 when the adhered toner is rubbed by the developer 110 in the developer container 108.
However, when toner of the type that can be fixed to a transfer sheet at a relatively low temperature is used in the developing device 104, because of its relatively strong adhering force, the toner adhered to the developing sleeve 109 is gradually fixed to the developing sleeve 109, and thereby an insulating layer is formed by the toner on the developing sleeve 109. Such an insulating layer of toner on the developing sleeve 109 causes a problem of hindering development of a latent image by the developing device 104.
The present invention has been made in view of the above-discussed and other problems and addresses the above-discussed and other problems.
Preferred embodiments of the present invention provide a novel image developing device of an image forming apparatus and a novel image forming apparatus using the developing device, that prevent toner that can be fixed to a transfer sheet at a relatively low temperature from adhering and being fixed to a developing sleeve of the developing device.
According to a preferred of the present invention, a novel image developing device of an image forming apparatus using a two-component developer including toner and carrier includes a developer stirring device configured to stir the developer so as to charge the toner, a developing sleeve configured to rotate and to carry on its surface the developer, and a conductive doctor blade that is grounded and is configured to regulate a thickness of the developer on the developing sleeve. An electric potential of the developing sleeve is set to a same electric polarity as that of the toner, and the toner of the developer carried on the developing sleeve is moved toward a latent image formed on a photoconductor of the image forming apparatus so as to adhere to the latent image by an electric field formed between the developing sleeve and the latent image on the photoconductor. An average particle diameter of the carrier is about 50 xcexcm or smaller, and a charge amount of the carrier after the developer has been stirred by the stirring device is about 15 xcexcc/g or greater.
Thus, in a novel image developing device of the present invention using a two-component developer and a reversal development system, a conductive doctor blade of the developing device is grounded so as to peel off toner adhered to a developing sleeve of the developing device, and carrier that has an average particle diameter of about 50 xcexcm or smaller and a charge amount of about 15 xcexcc/g or greater after the developer has been stirred by the developer stirring device is used so as to move toner adhered to the doctor blade to the carrier of the developer carried on the developing sleeve by the electric charge of the carrier. Thereby, even when toner that can be fixed to a transfer sheet at a relatively low temperature and that thereby has a relatively strong adhering force is used, the toner is prevented from adhering and being fixed to the developing sleeve.
According to another embodiment of the present invention, a novel image developing device of an image forming apparatus using a two-component developer including toner and carrier includes a developer stirring device to stir the developer so as to charge the toner, a developing sleeve configured to rotate and to carry the developer on its surface, and a conductive doctor blade configured to regulate a thickness of the developer on the developing sleeve. A voltage of an electric polarity opposite to that of the toner is applied to the doctor blade. The toner of the developer carried on the developing sleeve is moved toward a latent image formed on a photoconductor of the image forming apparatus so as to adhere to the latent image by an electric field formed between the developing sleeve and the latent image on the photoconductor. An average particle diameter of the carrier is about 50 xcexcm or smaller, and a charge amount of the carrier after the developer has been stirred by the developer stirring device is about 15 xcexcc/g or greater.
Thus, in a novel image developing device of the present invention using a two-component developer a voltage of a polarity opposite to that of toner is applied to a doctor blade of the developing device so as to peel off toner adhered to a developing sleeve of the developing device, and carrier that has an average particle diameter of about 50 xcexcm or smaller and a charge amount of about 15 xcexcc/g or greater after the developer has been stirred by the developer stirring device is used so as to move toner adhered to the doctor blade to the carrier of the developer carried on the developing sleeve by an electric charge of the carrier. Thereby, even when toner that can be fixed to a transfer sheet at a relatively low temperature and that has a relatively strong adhering force is used, the toner is prevented from adhering and being fixed to the developing sleeve.